Preparation of aryldihaloboranes and poly (dihaloborano) benzenes



3,092,652 Patented June 4, 1963 3,092,652 PREPARATION F ARYLDIHALGBORANES AND POLYmIiHALGBfiRANO) BENZENES David R. Stern, Fullerton, Lahrner Lynds, North Hollywood, and Robert M. Washburn, Whittier, Calif assignors to American Potash & Chemical Corporation, a corporation of Delaware No Drawing. Filed Jan. 16, 1959, Ser. No. 787,106 19 Claims. ((21. 260-452) This invention relates to the preparation of aryldihaloboranes, poly(dihaloborano)benzenes (including benzenes having nuclear hydrogens replaced with other radicals), and to the preparation of the corresponding boronic and polyboronic acids and to the corresponding alkyl esters of the boronic acids.

A number of uses are known for the areneboronic acids; see, for example, the article of Beran, Pray and Bohrn appearing in Mitt. Chem. Forsch. Inst., Wirtsch. Osterr, 6, 5456 (1952), wherein a wide variety of boronic acids were tested for insecticidal activity against the granary weevil and the house fly, among other insects. Virtually all of the materials tested against these insects to a greater dissolved in 95% alcohol at a concentration of 45.4 mg. per ml. and in both contact tests, wherein the house flies were allowed to directly contact filter papers which had been treated with the toxic material in solution, and in vapor toxicity tests, 100% of the flies were found dead or moribund after a period of 24 hours.

The areneboronic acids, both the monoborom'c acids and the polyboronic acids, also find use as antioxidants. They are thermally and hydrolytically stable and soluble in hydrocarbons and thus are especially suitable for use as antioxidants in petroleum oils or in other organic materials Where an antioxidant is desired. For example, they may be used as antioxidants for aniline, a material used in die making, wherein they inhibit the formation of color bodies which result from oxidation.

The aryldihaloboranes and poly(dihalobor-ano) benzenes which are treated as intermediates here are also known materials [with the exception of those of the formula Ar(BX and various other utilities for these known materials are recognized.

It has been discovered that aryldihaloboranes and poly- (dihaloborano) benzenes can be formed in high yields by a simple Friedel-Crafts type reaction between aromatic compounds and boron trihalides in the presence of an appropriate catalyst such as anhydrous aluminum chloride. The reactions can be represented by the following generalized equation:

ArH +nBX catalyst Ar(BX +nHX where n is an integer of between 1 and 3, X is Cl, Br; and Ar is an aromatic nucleus. The nucleus may be substituted with various substituents such as CH O, CICH C H etc., the only requirement being that the substituent not be so electronegative as to prevent reaction.

As shown in the examples, the molar ratio of catalyst to 3X falls within the range of 0.0374 to 0.0125.

Subsequent to the formation of the compound of the formula Ar(BX the reaction product may be hydrolyzed to form the corresponding arenemonoboronic or arenepolyboronic acid. Also, the compound of the formula Ar(BX may be treated with alcohol to form an ester of the formula Ar[B(OR) or the acid may be dehydrated to the anhydride.

As pointed out in greater detail below, mixtures of products may be prepared which have boron-containing groups substituted to greater or lesser extents on the aromatic nucleus; formation of either Ar(BX or Ar(BX or ArBX may be encouraged by varying the mole ratio of the reactants.

One-half mole percent of catalyst is sufficient to ensure that the reactron proceeds properly and the preferred ratio is determined readily. The concentration of catalyst determines the rate of reaction rather than the end result.

Any catalyst of the Friedel-Crafts type is suitable and preferred catalysts are AlBr AlCl FeCl SnCl BE, and ZnCl Many Friedel-Crafts type catalysts are available having varying degrees of activity and hence conthe entering groups tend to become oriented in ortho and para positions, whereas orientation obtains.

The products obtained depend on concentration or mole ratio of reactants and method of addition. Slow addition of boron trihalide to an excess of aromatic ma terial in the presence of aluminum chloride results in the formation of an :aryldihaloborane. The reverse procedure, in which the aromatic material is added to a large excess of boron trihalide, results in the formation of bis- (dihaloborano)benzene with small amounts of the tris and other more highly substituted materials. Intermediate ratios of reactants result in a mixture of the two primary products.

The reaction of a boron trihalide :with an aromatic material is exothermic and takes place quite readily. Preferably, reactions are initiated at about 45 C. and the temperature allowed to rise to about C. The higher reaction temperatures favor poly substitution and increase the speed of reaction. The reaction will proceed at about room temperature, but very slowly, while when the reaction mixture is heated above the boiling point, pressure out at reflux temperature.

A hydrogen halide is a by-product of both the reaction halides. poly(dihaloborano)- benzenes, etc., are liquids or low melting solids and can be recovered by distillation or crystallization. The hy drolysis products of the haloboranes are solids and are easily recovered by filtration. They can be purified by recrystallization from a suitable solvent. Yields as high as 93%, based on boron trihalide, may be realized provided the recovery system is sufiiciently efiicient. Yields of up to 40% benzenediboronic acid based on boron trihalide have been realized.

The entire group of compounds containing aryl-boron bonding is susceptible to both hydrolysis and oxidation. However, the aryldihaloboranes, unlike the alkyldihaloboranes, were found to be sufliciently stable so that standard handling techniques could be applied to the intermediates.

The practice of this process will become further apparent from the consideration of the following examples which are set forth by way of illustration.

EXAMPLE I. BENZENEBORONIC ACID Benzene (532 ml., 468 g., 6.0 moles) and aluminum chloride Morton flask. The flux (vapor 80.2 504 g., 2.0 moles) 10 grams of (0.075 mole) were placed in a 1-1 temperature was raised to mild re- C.) and boron tribromide ml., was added via a dropping funnel over a 2-hour period. .Copious evolution of hydrogen bromide (determined by infrared spectra) was immediately evident. A plot of hydrogen bromide liberated versus time was made in order to determine the reaction time. The

ml.) of hydrogen bromide was collected at -78 C., and provided a good indication that poly substitution had taken place. Excess reactants were separated by distillation as before. The distillation was terminated at 125 hours, attaining a final vapor temperature of 91 C., in dicating benzene had been essentially consumed. The reaction duration was increased to favor poly substitution. Vigorous agitation was used'at all times. During the course of reaction, 79 ml. (theory for disubstitution, 98

slope or rate of formation indicated that 4-6 hours was 5 C. (pot temperature) when it became evident that desufficient time for mono substitution. The reaction was composition of the intermediate was occurring. Rerun for a total of 5 hours and 55 ml. (theory, 45.5 ml.) actants were removed between 88 and 97 C. (Vapor) hydrogen bromide was trapped at -78 C. Actually, for a total volume of 285 ml. (694 g.). The reaction hydrogen bromide has considerable vapor pressure at mixture was cooled and transferred to a dropping funnel '78 C. (387 mm. Hg) and cannot be completely reand then added slowly to 500 ml. chilled 0.2 N hydrocovered by condensation. A Whitmore-Lux distillation chloric acid. Addition rate of 60 drops per minute prohead was then placed'on the reaction flask and the unreduced stronghydrogen bromide evolution and vapor temacted components were removed by distillation. The disperature of 84 C. The addition rate was reduced to 32 tillati-on was terminated at 130 C. (pot temperature) drops per minute, and vigorous agitation was employed when decomposition of the crude intermediate began. at all times. The mixture was then filtered as before, Reactants were removed between 80 and 92 C, (vapor) yielding 150 grams crude material. The crude product for aitotal volume of 430 ml. (455 g.). The flask was was extracted with 400 ml. ether. The solids were discooled and the intermediate transferred to a dropping solved in 400 ml. of hot water, the resulting aqueous solufunnel. It was then a dad slowly (50 mL/hour) into 500 tion filtered hot, and the filtrate was allowed to cool. ml. of 0.2 N hydrochloric acid maintained near 0 C. Four crops of crystals were obtained in the course of with continuous agitation. After addition of 100 ml. successive Work-ups for a total of 113 grams. The ether phenyldibromoborane, solids began to appear. Upon extract was reduced to 100 ml. and an equal volume of completion of the addition, the solids were removed by distilled water was added. More ether was removed until filtration and appeared as small gray spheres. The dried only a small layer remained containing some solids. It crude product weighed 192 grams. Spectra of this ma was then filtered hot and allowed to cool. Crystals terial indicated practically pure benzeneboronic anhyformed from the filtrate which weighed 16.0 grams. A dride. The product was converted to benezeneboronic yield of 40.6% 1,3-benzenediboronic acid was obtained. acid by extraction with, ether and crystallization from Analysis-Cal for G 4[= )2]2 13-0 C, water. 43.48%; H, 4.83%. Found: B, 12.4%; C, 42.0%; H,

Analysis-Calc'd. for C H B(OH) B, 8.87%; C, 4.81.

59.06%; H, 5.74%; B-C/B (HgCl decomp.) 1.00. Benzenediboronic acids are not easily dehydrated even Found: B, 9.14%; C, 61.55%; H, 5.93%; B-C/ B (HgCl at fairly high temperatures'and can be readily handled at id 1.00, room temperature without special techniques.

The analytical data indicate slight dehydration of the Various additional reactions were carried out wherein product to the anhydride. A portion of this material was different aromatic compounds were allowed to react with reconvened to the anhydride by redissolving in ether and boron. tribromide- I each instance, h b r n ribroevaporating to dryness to insure complete dehydration. mide, the aromatic compound, and the aluminum chlo- Analysin-Calcd. for (C H BO) B, 10.42; C, ride catalyst Were heated under reflux. The reaction fol- 69.36%; H, 4.82%; B-C/B (HgCl decomp.) 1.00. lowed; hydrogen bromide was liberated. The ratio of F d; 13, 101%; C, 68 5()%; H, 5.31%, -BBr :arene was adjusted to approximately 1.0 where Since the anhydride'is the most stable species, it served a predominantly monoboronic acid product w s desir d as a basis for calculations. Calculated yield basedon and Was adjusted Closer to -0 h re a predominantly dibo n tibro id used was 93%, boronic acid product was desired. Where significant quantities of a triboronic acid are desired, the ratio must EXAMPLE IL-BENZENEDIBORONIC ACID be adjustsd to at least 3.0.

Boron tribromide (568 ml., 1505 g., 6.0 moles) and The data set forth in the table below indicate that a 10 grams of anhydrous aluminum chloride were placed in mixture of monoand diboronic acids was formed in the a 11,M,ortonflask. The temperature was raised to mild case of the toluene and biphenyl and only monoboronic reflux and benzene (177 ml., 156 g., 2.0 moles) was acid was formed in the case of the chlorobenzene and added slowly over a 2-hour period via a dropping funnel. naphthalene. The quantities, ratios, reagents, etc., used The mixture was gently heated under refluxing for 24 are set forth in Table'A below.

Table A Alon Time Obsv. Run Reactant Catalyst, Reactant, Halide, Heating, Ratio No. Grams Moles Moles Hrs. BBrg: Arcne As is seen from the examples above, the aryl-B compounds may readily be recovered by hydrolysis of the.

intermediate aryldihaloborane or poly(dihaloborano)- benzene (or nuclear-substituted benzene).

The dihaloborano materials may also be distilled off and recovered as such, or esters may be formed from the acids described in the examples above and these may he recovered by distillation.

The preparation of a typical aryldihaloborane and the recovery thereof by distillation is set forth in Example IV below.

The intermediate aryldihaloboranes and poly(dihaloborano)benzenes may also be treated with alcohol and water to form the monoboronic and polyboronic acids. The alcohol is added slowly to the intermediate and the resulting ester is subsequently hydrolyzed so as to form the acid. Alternatively, the ester may be used as such as an antioxidant in the same manner as the corresponding acid. An example showing the esterification of one of the intermediates is set forth below as Example 111.

EXAMPLE IIL-PREPARATION OF DIMETHYL BENZENEBORONATE This reaction can be performed in almost any inertv solvent or in an excess of the alcohol.

Obviously, many modifications and variations of this,

invention may be made without departing from the spirit and scope thereof and only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for the tween 1 and 3, class consisting of aryl and haloaryl comprising: forming a mixture of a Friedel-Crafts catalyst and a boron trihalide of the general formula BX the molar ratio of said catalyst to said BX being within the range 0.03 74-0.0125, adding thereto a quantity of the compound of the formula ArH heating the mixture so formed whereby to react said BX and ArH to form said Ar(BX and gaseous HX and withdrawing said gaseous HX therefrom as said HX is formed.

2. The process of claim 1 wherein Ar is C H n is 1 and X is Cl.

3. The process of claim 1 wherein Ar is C H n is 1 and X is Br.

4. The process of claim 1 wherein ArH 5. The process of claim 1 wherein ArH is C H C H 6. The process of claim 1 wherein ArH is C H Cl.

7. The process of claim 1 wherein ArH, is naphthalene.

8. The process of claim 1 wherein ArH is C H 9. The process of claim 1 wherein Ar is C H n is 2 and X is Cl.

10. The process of 2 and X is Br.

11. The process of claim 1 wherein the Ar(BX is thereafter hydrolyzed to Ar[B (OH) 12. The process of claim 1 wherein the Friedel-Crafts catalyst is aluminum trichloride.

13. The process of claim 1 wherein the Friedel-Crafts catalyst is aluminum tribromide.

14. The process of claim 1 wherein the Friedel-Crafts catalyst is ferric chloride.

15. The process of claim 1 wherein the Friedel-Crafts catalyst is zinc chloride.

16. The process of claim 1 wherein the Ar(BX so formed is reacted with a lower alkyl alcohol of the formula ROH where R is lower alkyl to form Ar[B(OR) 17. The process of claim 11 wherein ROH is CH OH.

18. The process of claim 11 wherein X is Cl.

19. The process of claim 11 wherein X is Br.

References Cited in the file of this patent UNITED STATES PATENTS Muetterties Aug. 18, 1959 OTHER REFERENCES Torssell: Acta Chem. Scan, vol. 8, pp. 1779-86 (1954).

Nielsen et al.: J. Am. Chem. Soc., vol. 79, pp. 30814 (1957).

Muetterties: J. Am. Chem. Soc., vol. 81, p. 2807, May 20, 1959.

claim 1 wherein Ar is C H n is 

1. A PROCESS FOR THE PREPARATION OF COMPOUNDS OF THE GENERAL FORMULA AR(BX2)N WHEREIN N IS AN INTEGER BETWEEN 1 AND 3, X IS HALOGEN AND AR IS SELECTED FROM THE CLASS CONSISTING OF ARYL AND HALOARYL COMPRISING: FORMING A MIXTURE OF A FRIEDEL-CRAFTS CATALYST AND A BORON TRIHALIDE OF THE GENERAL FORMULA BX3, THE MOLAR RATIO OF SAID CATALYST TO SAID BX3 BEING WITHIN THE RANGE 0.0374-0.0125, ADDING THERETO A QUANTITY OF THE COMPOUND OF THE FORMULA ARHN, HEATING THE MIXTURE SO FORMED WHEREBY TO REACT SAID BX3 AND ARHN TO FORM SAID AR(BX2)N AND GASEOUS HX AND WITHDRAWING SAID GASEOUS HX THEREFROM AS SAID HX IS FORMED.
 16. THE PROCESS OF CLAIM 1 WHEREIN THE AR(BX2)N SO FORMED IS REACTED WITH A LOWER ALKYL ALCOHOL OF THE FORMULA ROH WHERE R IS LOWER ALKYL TO FORM AR B(OR)2!N. 